I am using linux v2.0.33. In
/usr/src/linux/arch/i386/kernel/entry.S
SYMBOL_NAME slots 164,165,166 are as follows:
.long 0,0
.long SYMBOL_NAME(sys_vm86)
I found that I could not add a new system call at 167. When
I did, it was called by something else for who knows what
reason. I know this because the only thing in my new system
call was a printk statement (which displays whenever the new
system call is called). With the system call at 167 I would
receive unwanted printk messages at boot time, at shutdown
time, and when I executed ifconfig! Hence, I put the
following at 167 and put my new system call at 168.
.long 0
That seems to have made everything work! Another strange
thing is that with my system call at 167 the insmod
function reports "unresolved symbol" messages and will not
install modules?? My guess is that one of the modutil
modules is using the 167 slot! Anyone have any ideas?
Regarding printk:
It is my understanding that printk messages will appear on
the console (I am assuming you are at a console if you are
modifying system calls and generating the kernel ) as long
as your message level is less then your log level. I use
<0> for testing to be sure of having the lowest message level.
For example:
printk("<0>syscallname: entering my test syscall\n");
This works for me.